The present invention relates to a reflection type diffuse hologram that can be used for display devices such as liquid crystal display devices, a hologram for reflection hologram color filters, etc., and a reflection type display device using such holograms.
Backlight used with a liquid crystal display device should have some scattering characteristics, so that the display device can have a wide viewing angle. So far, scattering characteristics have been imparted to backlight by use of beads or the like, but a problem with this is that too large an angle of diffusion results in wasteful illumination light loss.
This is also true of an automotive brake lamp or direction indicator. That is, although too large a diffusion angle is not required in view of the positional relation to succeeding cars, light from these lamps is not only wastefully consumed but also becomes dark because lenses positioned in front of the lamps cause the light to be diffused at an angle larger than required.
The present applicant has filed Japanese Patent Application No. 12170/1993 to come up with a color filter in which a hologram is used to achieve a remarkable increase in the efficiency of backlight used for liquid crystal display purposes, etc., and a liquid crystal display device that makes use of such a color filter.
A typical liquid crystal display device that makes use of this hologram color filter will now be briefly described with reference to a sectional view attached hereto as FIG. 43. As illustrated, a hologram array 55 forming the color filter is spaced away from the side of a liquid crystal display element 56 upon which backlight 53 is to strike, said element being regularly divided into liquid crystal cells 56xe2x80x2 (pixels). On the back side of the liquid crystal display element 56 and between the liquid crystal cells 56xe2x80x2 there are located black matrices 54. Although not illustrated, polarizing plates are arranged on the incident side of the hologram array 55, and the exit side of the liquid crystal display element 56. As is the case with a conventional color liquid crystal display device, between the black matrices 54 there may additionally be located an absorption type of color filters which transmit light rays of colors corresponding to pixels R, G, and B.
The hologram array 55 comprises micro-holograms 55xe2x80x2 which are arranged in an array form at the same pitch as that of R, G, and B spectral pixels, corresponding to the period of repetition of R, G, and B spectral pixels, i.e., sets of liquid crystal cells 56xe2x80x2, each including three adjoining liquid crystal cells 56xe2x80x2 of the liquid crystal display element 6 as viewed in a plane direction of the drawing sheet. One micro-hologram 55xe2x80x2 is located in line with each set of three adjoining liquid crystal cells 56xe2x80x2 of the liquid crystal display element 6 as viewed in the plane direction of the drawing sheet. The micro-holograms 55xe2x80x2 are then arranged in a Fresnel zone plate form such that a green component ray of the backlight 3 incident on the hologram array 55 at an angle xcex8 with respect to its normal line is collected at a middle liquid crystal cell G of the three R, G, and B spectral pixels corresponding to each micro-hologram 55xe2x80x2. Each or the micro-hologram 55xe2x80x2 in this case is constructed from a relief, phase, amplitude or other transmission type of hologram which has little, if any, dependence of diffraction efficiency on wavelength. The wording xe2x80x9clittle, if any, dependence of diffraction efficiency on wavelengthxe2x80x9d used herein is understood to refer specifically to a hologram of the type which diffracts all wavelengths by one diffraction grating, much unlike a Lippmann type hologram which diffracts a particular wavelength alone but does not substantially permit other wavelengths to be transmitted therethrough. The diffraction grating having little dependence of diffraction efficiency on wavelength diffracts different wavelengths at different angles of diffraction.
In such an arrangement, consider now the incidence of the white backlight 3 from the side of the hologram array 55, which does not face the liquid crystal display element 56 at the angle xcex8 with respect to its normal line. The angle of diffraction of the light by the micro-hologram 55xe2x80x2 varies depending on wavelength, so that light collection positions for wavelengths are dispersed in a direction substantially parallel with the surface of the hologram array 55. If the hologram array 55 is constructed and arranged such that the red wavelength component is diffractively collected at a red-representing liquid crystal cell R; the green wavelength component at a green-representing liquid crystal cell G; and the blue wavelength component at a blue-representing liquid crystal cell B, the color components pass through the corresponding liquid crystal cells 56xe2x80x2 with no or little attenuation through the black matrices 4, so that color displays can be presented depending on the state of the liquid crystal cells 56xe2x80x2 at the corresponding positions. It is here noted that the angle of incidence xcex8 of backlight 53 on the hologram array 55 is determined by various conditions including hologram-recording conditions, the thickness of hologram array 55, and the distance between the hologram array 55 and the liquid crystal display element 6.
By using the hologram array 55 as a color filter in this way, the wavelength components of backlight used with a conventional color filter are allowed to strike on the liquid crystal cells 56xe2x80x2 without extravagant absorption, so that the efficiency of utilization thereof can be greatly improved.
The aforesaid hologram color filter proposed by the present applicant is applicable to only a color liquid crystal display device making use of backlight. However, when surrounding ambient light alone is used as illumination light, this hologram color filter cannot diffract, and collect its wavelength components into desired positions. In other words, this hologram color filter can never be applied to a direct-view type of liquid crystal display device or other like device in which surrounding ambient light is used as illumination light, or any particular backlight source is not required.
Moreover, the applicant has filed Japanese Patent Application No. 120016/1993 to come up with a method for using a swelling film to make from a volume hologram having uniform interference fringes recorded therein a color pattern that varies in reconstructed color depending on position. The principles are similar to those applied to a photopolymer. First, a swelling film is prepared by mixing a monomer or oligomer, a photopolymerization initiator, etc. with a binder polymer. Then, the swelling film is irradiated with a given quantity of light before or after its close contact with a photopolymer or other photosensitive material having interference fringes recorded therein, so that a given proportion of the monomer or oligomer contained in the swelling film, on the one hand, is polymerized for deactivation and the amount of the remaining active monomer or oligomer, on the other hand, is controlled. The thus controlled amount of the monomer or oligomer is diffused, and swollen into the photosensitive material with interference fringes recorded therein, whereby fringe spacings are precisely controlled to any desired quantity to control reconstruction wavelengths to given ones. After this swelling treatment, the photosensitive material with the interference fringe recorded therein is irradiated with light or otherwise heated to fix the diffused monomer or oligomer in the interference fringes, so that there can be obtained a hologram excelling in the storage stability of reconstructed colors. In addition, a color pattern can be formed on the hologram by allowing the illumination light to have a spatial distribution.
This method will now be explained in a little more detail with reference to FIGS. 44 and 45. FIG. 44 illustrates the principles applied when the swelling agent (monomer or oligomer) contained in the swelling film is deactivated by irradiation with light after the swelling film has been brought into close contact with the photosensitive material, and FIG. 45 depicts the principles applied when the swelling agent contained in the swelling film is deactivated by irradiation with light before the swelling film is brought into close contact with the photosensitive material. Referring to FIG. 44(a), such a volume hologram 64 as depicted in FIG. 44(b) is obtained by striking object light 62 and reference light 63 on both sides of a photopolymer or other photosensitive material 61 to record an interference fringe therein. As depicted in FIG. 44(c), a swelling film 65 prepared by mixing a monomer or oligomer, a photopolymerization initiator, etc. with a binder polymer is then brought into close contact with the photosensitive material. Subsequently, either the hologram 64 or the swelling film 65 is irradiated with light 66, as depicted in FIGS. 44(d1) to (d3), before or at the same time as heating is carried out to increase the degree of diffusion of the penetrating monomer or oligomer in the swelling film 65. This irradiation with light 66 causes a part or all of the penetrating active monomer or oligomer in the swelling film 65 to be polymerized, and so deactivated, at a proportion corresponding to the quantity of irradiating light 66, so that the ability of the monomer or oligomer to penetrate (diffuse) vanishes substantially. When the quantity of irradiating light 66 is large (FIG. 44(d1)), therefore, nearly all of the penetrating active monomer or oligomer in the swelling film 65 is deactivated, so that the monomer or oligomer does not substantially penetrate into the hologram 64 even upon heated. If, for instance, interference fringes are recorded in the volume hologram 64 with a blue wavelength in FIG. 44(a), the hologram 64 subject to the swelling step in FIG. 44(d1) does not substantially swell, and diffracts and reconstructs blue light. When the quantity of irradiating light 66 is moderate (FIG. 44(d2)), on the other hand, about a half of the penetrating active monomer or oligomer in the swelling film 65 is deactivated. Another half of the penetrating monomer or oligomer penetrates into the hologram 64 upon heated, which in turn swells moderately. For this reason, the hologram 64 subject to the swelling step shown in FIG. 44(d2) diffracts, and reconstructs green light that is longer in wavelength than blue light. Moreover, when the swelling film is not irradiated with light 66 (FIG. 44(d3)), nearly all of the penetrating monomer or oligomer from the swelling film 65 penetrates into the hologram 64, which in turn swells to the maximum extent. For this reason, the hologram 64 subject to the swelling step shown in FIG. 44(d3) diffracts, and reconstructs red light that is longer in wavelength than green light. By controlling the quantity of light 66 with which the swelling film 65 into close contact with the hologram 64 is irradiated, it is thus possible to optionally regulate the color to be reconstructed to one lying between red and blue.
Referring then to FIG. 45, especially FIGS. 45(a) and 45(b), a volume hologram 64 is obtained as depicted in FIGS. 44(a) and (b). As shown in FIGS. 45(c1) through (c3), a swelling film 65 is prepared by mixing a monomer or oligomer, a photopolymerization initiator, etc. with a binder polymer. Upon this film irradiated with a given quantity of light 66, a part or all of the penetrating active monomer or oligomer contained therein is deactivated at a proportion corresponding to the quantity of light 66, so that the ability of the monomer or oligomer to penetrate (diffuse) vanishes. When the swelling film 65 already irradiated with light 66 is brought into close contact with the hologram 64, as depicted in FIGS. 45(d1) through 45(d3), and then heated as shown in FIG. 44, the degree of swelling of the hologram 64 varies depending on the quantity of light 66. By controlling the quantity of light 66 with which the swelling film 65 is irradiated, it is thus possible to optionally regulate the color to be reconstructed to one lying between red and blue.
In this regard, it is noted that the swelling film 65 is prepared by mixing a monomer or oligomer, a photopolymerization initiator, etc. with a binder polymer, and so is similar to a photopolymer used for recording holograms. Therefore, the hologram-recording photopolymer may be used as the swelling film 65; that is, it is unnecessary to prepare any special swelling film.
The aforesaid color pattern-making method proposed by the present applicant is to control the quantity of light with which the swelling film is irradiated before or after it is brought into close contact with a photosensitive material having interference fringes already recorded therein, thereby controlling the amount of the active monomer or oligomer contained in the swelling film, so that the proportion of swelling of the interference fringes (or the interference fringe spacings) can be controlled to regulate the color to be reconstructed to a given one. In short, the color to be reconstructed is controlled by the quantity of irradiating light.
However, one problem with the aforesaid method is that it is not always easy to precisely control the quantity of light to develop a given color, and another possible problem is that the reproducibility of the color reconstructed is not stable.
In view of such problems associated with the prior art, it is an object of the present invention to provide a diffusing plate which can use a hologram to limit the angle of diffusion within a desired range, and makes bright display, etc. possible.
Another object of the present invention is to provide a reflection type of direct-view color display device such as a color liquid crystal display device, which makes use of a hologram color filter already proposed by the present applicant but makes no use of any backlight source at all.
Yet another object of the present invention is to provide a reflection type color display device such as a color liquid crystal display device, which uses a hologram reflection layer as a color filter but makes no use of any backlight source.
Still yet another object of the present invention is to provide a hologram recording medium, and a hologram color display medium, which can all be utilized as a color filter of a reflection type color display device, and a method of making them.
According to the present invention, the objects mentioned above can be achieved by the provision of a reflection type diffuse hologram characterized by reflecting, and diffracting light incident thereon at an angle with respect to a normal direction while it is diffused within a desired angle range. Throughout the specification, it is to be noted that the angle of incident light with respect to the normal direction may include 0xc2x0, or the angle of incidence may be 0xc2x0.
In this case, it is desired that the angle of diffusion lie within a range of 10xc2x0 to 35xc2x0.
Another reflection type diffuse hologram of the present invention is characterized by having been formed by allowing diffused light that diffuses within a desired angle range, and parallel light to strike on both sides of a volume hologram-recording photosensitive material, and interfere therein.
It is here to be noted that an image has simultaneously been recorded in the reflection type diffuse hologram of the present invention in a recontructible fashion.
It is also to be noted that the reflection type diffuse hologram may be located on a backlight side of a liquid crystal display device for diffuse illumination purposes.
The present invention provides a method for fabricating a reflection type diffuse hologram characterized in that a transmission type diffusing plate having a diffusion angle characteristic within a desired angle range is located in close contact with, or in proximity to, a volume hologram-recording photosensitive material, and two light beams are allowed to strike on front and back sides of the combined diffusing plate and photosensitive material for interference recording.
In this case, the transmission type diffusing plate used may be a diffusing plate of a 20% to 60% haze, an array of microlenses, a lenticular screen or the like.
A reflection type of direct-view color display device using a hologram color filter according to the present inventionxe2x80x94which is provided to achieve the objects mentioned abovexe2x80x94comprises a hologram color filter composed of an array of element light-collecting holograms, each of said element light-collecting holograms comprising a hologram color filter for subjecting white light incident at a given angle with respect to a normal line of a hologram-recorded surface to wavelength dispersion in a direction substantially along said hologram-recorded surface for spectral diffraction, a reflection type hologram located in the vicinity of a light-collection surface thereof, and a transmission type spatial light modulator located between said hologram color filter and said reflection type hologram.
In this case, it is preferable that the reflection type hologram has interference fringes recorded in the vicinity of a position on which white light strikes while said white light is separated into each spectral component of each color, said interference fringes reflecting light of wavelength of each color in an identical direction.
The reflection type hologram may be of diffusibility.
For the transmission type spatial light modulator, for instance, a liquid crystal display element may be used.
A reflection type color display device of the present inventionxe2x80x94which is provided to achieve the aforesaid objectxe2x80x94is characterized by comprising a transmission type spatial light modulator comprising a collection of pixels, and having a controllable transmittance per pixel, and a reflection type hologram color filter located on a back side of said modulator.
In this case, it is preferable that the reflection type hologram color filter comprises periodically arranged volume hologram elements varying in reflection, and diffraction wavelength for each position of the pixels in the transmission type spatial light modulator.
In this connection, the reflection type hologram color filter may be of diffusibililty.
It is preferable that the reflection type hologram color filter has an absorption layer located on a back side thereof.
Also, the reflection type hologram color filter may be provided on its back side with an absorption type color filter, which is provided on its back side with a backlight source, so that color information is interchangeable when said backlight source is turned on, said color information being displayed on each pixel in the transmission type spatial light modulator.
It is here noted that for the transmission type spatial light modulator, for instance, a liquid crystal display element, a polymer-dispersed type liquid crystal display element or the like may be used.
A hologram-recorded medium of the present inventionxe2x80x94which is provided to achieve the aforesaid objectxe2x80x94is an imagewise or other pattern-recorded medium comprising a collection of pixels, characterized in that any one of a plurality of volume type diffraction gratings comprising volume holograms and differing from each other is assigned to at least a part of said pixels.
In this case, it is preferable that a plurality of volume type diffraction gratings comprising volume holograms and differing from each other include at least three volume type diffraction gratings which are identical in orientation of grating surface with each other but different in grating spacing from each other.
It is also preferable that at least two of a plurality of mutually different volume type diffraction gratings are multi-recorded in at least a part of the pixels.
It is further preferable that a volume type diffraction grating that expresses red, a volume type diffraction grating that expresses green, and a volume type diffraction grating that expresses blue are assigned to three dot areas into which at least a part of the pixels is divided, or to three adjoining pixels, so that color tone or gradation is controlled by varying a dot percent occupied by said volume type diffraction gratings, or a diffraction efficiency ratio between said volume type diffraction gratings.
The hologram-recorded medium of the present invention may have a reflecting layer on its back side.
Each of pixels in the hologram-recorded medium of the present invention may be of diffusibility.
The hologram-recorded medium of the present invention as mentioned above may be used as a reflection type hologram color filter.
Such a hologram-recorded medium of the present invention is fabricated as recited below.
(1) A method of fabricating a hologram-recorded medium characterized by stacking a volume hologram photosensitive material on a reflection type relief hologram, and striking reconstructing illumination light of given wavelength on said reflection type relief hologram through said volume hologram photosensitive material, so that interference fringes produced by interference of light diffracted from said reflection type relief hologram and the incident light are recorded in said volume hologram photosensitive material.
(2) A method of fabricating a hologram-recorded medium characterized by stacking a volume hologram photosensitive material on a transmission type hologram, and striking reconstructing illumination light of given wavelength on a side of said transmission type hologram that is not opposite to said volume hologram photosensitive material, so that interference fringes produced by interference of light diffracted from said transmission type hologram and reference light incident on said volume hologram photosensitive material are recorded in said volume hologram photosensitive material.
(3) A method of fabricating a hologram-recorded medium characterized by stacking a volume hologram photosensitive material on a transmission type hologram, and striking reconstructing illumination light of given wavelength on a side of said transmission type hologram that is not opposite to said volume hologram photosensitive material, so that interference fringes produced by interference of light diffracted from said transmission type hologram and zero-order transmitted light are recorded in said volume hologram photosensitive material, followed by provision of a reflecting layer on a back side of said volume hologram photosensitive material.
(4) A method of fabricating a hologram-recorded medium characterized by locating a mask plate having an opening pattern on one side of a volume hologram photosensitive material and a reflecting mirror on another side of said volume hologram photosensitive material, said reflecting mirror having a specific angle of inclination with respect to said volume hologram photosensitive material, and striking a light beam on said volume hologram photosensitive material through said opening pattern in said mask plate, so that interference fringes produced by interference of the incident light and light reflected from said reflecting mirror are recorded in said volume hologram photosensitive material.
(5) A method of fabricating a hologram-recorded medium characterized by locating a mask plate having an opening pattern on one side of a volume hologram photosensitive material and an off-axis reflection type hologram on another side of said volume hologram photosensitive material, said off-axis reflection type hologram diffracting a light beam incident at a given angle of incidence in an opposite direction at a specific angle with respect thereto, and striking a light beam on said volume hologram photosensitive material through said opening pattern in said mask plate, so that interference fringes produced by interference of the incident light and light diffracted from said off-axis reflection type hologram are recorded in said volume hologram photosensitive material.
(6) A method of fabricating a hologram-recorded medium characterized by locating a composite reflector comprising a collection of micro-mirror surfaces varying in reflection direction per position on a back side of a volume hologram photosensitive material, and striking a light beam on a surface side of said volume hologram photosensitive material, so that interference fringes produced by interference of the incident light and light reflected from said composite reflector are recorded in said volume hologram photosensitive material.
(7) A method of fabricating a hologram-recorded medium characterized by striking two coherent thin light beams at a position of each of pixels in a volume hologram photosensitive material while said beams intersect at a relative angle corresponding to said position, thereby recording in said volume hologram photosensitive material interference fringes having an inclination and a pitch depending on said pixel position.
The hologram color display medium of the present inventionxe2x80x94which is provided to achieve the aforesaid objectionxe2x80x94is a hologram color display medium having interference fringes of light recorded in a thickness direction of a film, characterized by using two swelling films each containing a penetrating monomer or oligomer that is diffusible externally from a surface of said film, said penetrating monomer or oligomer being deactivated according to a given deactivation pattern, so that said hologram is swollen by said penetrating monomer or oligomer diffused from both surfaces of said hologram at different degrees of swelling depending on position.
In this case, it is preferable that the aforesaid two swelling films are brought into close contact with both surfaces of the aforesaid hologram, so that a two-dimensional diffraction pattern of two or more colors is obtained by the combination of a deactivation pattern of one swelling film with that of another swelling film.
A color image may be expressed by means of a collection of color display micro-units, each comprising a combination of two or more micro-pixels displaying two or more different colors, and the dot percent of dots in each color display micro-unit may be varied to express each color display micro-unit in any desired color by additive color mixing. If, in this case, the interference fringes recorded in the hologram is designed such that diffraction efficiency changes depending on the positions of the color display micro-units, or the hologram itself or its diffraction-side surface is designed such that absorptance changes depending on the positions of the color display micro-units, it is then possible to control the brightness or luminance of each color display micro-unit.
It is preferable that the hologram is a volume phase type hologram, and it is then preferable that the hologram is a hologram recorded in a photopolymer.
Also, the hologram color display medium of the present invention may be of diffusibility.
Such a hologram color display medium of the present invention as mentioned above may be used in the form of a reflection type hologram color filter.
Further, the present invention provides a first method of fabricating a hologram color display medium including a hologram having interference fringes of light recorded in a thickness direction of a film, wherein two swelling films each containing a penetrating monomer or oligomer that is diffusible externally from a surface of said film, said penetrating monomer or oligomer being deactivated according to a given deactivation pattern, are used so that said hologram is swollen by said penetrating monomer or oligomer diffused from both surfaces of said hologram at different degrees of swelling depending on position, characterized in that before or after the close contact of the two swelling films, in which the penetrating monomer or oligomer contained in that position is deactivated by irradiation of a given or more quantity of light, with both surfaces of said hologram, said two swelling films are irradiated according to said given deactivation pattern with a given or more quantity of light, and said hologram with the thus deactivated swelling films brought into close contact with both surfaces thereof is heated, thereby diffusing said penetrating monomer or oligomer from active areas of said swelling films into said hologram.
Furthermore, the present invention provides a second method of fabricating a hologram color display medium including hologram having interference fringes of light recorded in a thickness direction of a film, wherein two swelling films each containing a penetrating monomer or oligomer that is diffusible externally from a surface of said film, said penetrating monomer or oligomer being deactivated according to a given deactivation pattern, are used so that said hologram is swollen by said penetrating monomer or oligomer diffused from both surfaces of said hologram at different degrees of swelling depending on position, characterized in that before or after the close contact of one swelling film, in which the penetrating monomer or oligomer contained in that position is deactivated by irradiation of a given or more quantity of light, with one surface of said hologram, said one swelling film is irradiated according to said given deactivation pattern with a given or more quantity of light; said hologram with the thus deactivated swelling film brought into close contact with said one surface is heated, thereby diffusing said penetrating monomer or oligomer from an active area of said one swelling film into said hologram; before or after the close contact of another swelling film, in which the penetrating monomer or oligomer contained in that position is deactivated by irradiation of a given or more quantity of light, with another surface of said hologram, said another swelling film is irradiated according to said given deactivation pattern with a given or more quantity of light; said hologram with the thus deactivated swelling film brought into close contact with said another surface is again heated, thereby diffusing said penetrating monomer or oligomer from an active area of said another swelling film into said hologram.
In these methods, it is preferable that the hologram is a volume phase type hologram, and it is then preferable that the hologram is a hologram recorded in a photopolymer.
Furthermore, the present invention provides another multicolor hologram display unit comprising volume holograms multi-recorded therein, said volume holograms diffracting light of at least two different wavelengths, characterized by further comprising a color tuning film containing a penetrating monomer or oligomer that is diffusible from a surface thereof to an outside thereof, said penetrating monomer or oligomer being deactivated according to a given deactivation pattern, so that said monomer or oligomer is diffused from said color tuning film, whereby a portion of said volume holograms in no alignment with said deactivated pattern is swollen to diffract light of a wavelength that is different from a wavelength that is diffracted by a portion of said volume holograms in alignment with said deactivated pattern.
Preferably, the multi-recorded volume holograms are recorded all over a surface thereof, while the deactivation pattern comprising dots. This multicolor volume hologram display unit may be used as a hologram reflecting and scattering plate for liquid crystal display apparatus. The multicolor volume hologram display unit may also include an area having a different dot percent.
Preferably, the multi-recorded volume holograms are each recorded in a separate pattern area. In this case, an area swollen by the color tuning film and an unswollen area provide dots wherein red, green, and blue colors are reconstructible. The multicolor volume hologram display unit may also include an area having a different dot area.
The color tuning film may be integrally provided on the multicolor hologram display unit.
It is to be noted that the foregoing multicolor hologram display unit of the invention may be used as a reflection type hologram color filter.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.